The invention relates to a mechanical transmission comprising a frame, a first shaft which is rotatably connected to the frame and to which is fixed a pair of friction wheels placed at a mutual distance, a second shaft which is connected to the frame for rotation parallel to the first shaft and which carries a wheel which co-acts with an annular element comprising a circular contact surface located axially between the friction wheels of the first shaft, wherein the friction wheels comprise mutually converging friction surfaces.
Such a mechanical transmission is described in European patent application no. EP 94.910064.8 in the name of the same applicant as for the present invention.
The present invention has for its object to provide improvements and additions to a construction of the type described above. The invention provides for this purpose a transmission wherein the transmission comprises guide means for realizing a rotational translating movement of the wheel which is connected to the second shaft, which guide means are assembled from at least two linear guide tracks received mutually perpendicularly in a plate and guide elements co-acting with the linear guide tracks, wherein guide elements are connected to the wheel for rotational translation and guide elements are rigidly connected to the frame whereby the plate is movable in linear manner relative to the frame and the wheel is displaceable in linear manner relative to the plate.
It is known to use a planetary or differential system, such as for instance a plurality of planetary wheels for driving by a sun wheel and having an eccentric cam fixed to the wheel for rotational translation. A rotational translating movement is understood to mean a rotating movement of the wheel round an axis lying perpendicularly of the wheel and intersecting a plane through the wheel at a distance from the centre of the wheel. The wheel herein does not rotate relative to the centre of the wheel, i.e. the orientation of the wheel does not change during the rotational translating movement. The invention provides a transmission which can be manufactured much more advantageously.
The present invention also provides a mechanical transmission wherein the transmission comprises adjusting means for adjusting the eccentricity of the wheel connected to the second shaft relative to the first shaft, which adjusting means are formed by a rotatable and fixable eccentric. Such an eccentric which is simple to adjust enables variation in simple manner of the transmission ratio in a range which in principle is infinite, wherein it is also possible to cause the first shaft to stand still or to rotate in a direction opposed to that of the second shaft.
The invention moreover provides a mechanical transmission wherein the friction wheels are supported externally by nuts, which nuts are provided with contact surfaces which co-act with contra-contact surfaces arranged close to the external edge of the friction wheels. The contact surfaces and contra-contact surfaces preferably form parts of a helix. Even more preferably the nuts are placed under a bias in a direction toward each other, whereby the annular element can be clamped with a predetermined force between the friction wheels, whereby as the couple increases the pressure between the annular element and the friction wheels increases. In other words: the pressure with which the annular element is clamped between the friction wheels depends on the applied couple. Supporting of the friction wheels close to the outer end has the advantage that the converging form of the mutually facing sides of the friction wheels will not change when extremely great forces are exerted on the friction wheels.
Finally, the present invention provides a mechanical transmission wherein the wheel makes internal contact with the annular element, whereby a radially inward facing surface forms a surface for coaction with the wheel. Using this "mirror-symmetrical" construction a very compact transmission can be realized which can for instance be built into a hub. Particularly envisaged herein are the hubs of cycles, but many other applications are of course also conceivable.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.